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Mendelian Genetics – inheritance of traits

Mendelian Genetics – inheritance of traits. Why Peas??. Many varieties (character, traits) Easy to control pollination Could choose distinct characters. First Experiments:. True-breeding parent generation. Why aren’t all the floweres light purple?. Mendel’s Law of Segregation.

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Mendelian Genetics – inheritance of traits

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  1. Mendelian Genetics – inheritance of traits

  2. Why Peas?? • Many varieties (character, traits) • Easy to control pollination • Could choose distinct characters

  3. First Experiments: True-breeding parent generation Why aren’t all the floweres light purple?

  4. Mendel’s Law of Segregation • White “heritable factor” did not disappear in F1 generation but only purple “heritable factor” was acting. • Alternative version of genes (heritable factors) account for variations in inherited characters. • For each character, an organism inherits two alleles (versions of the gene) one from each parent. • If the two alleles differ, one is fully expressed – DOMINANT; the other does not affect the organism’s appearance - RECESSIVE trait. • The two alleles segregate during gamete production

  5. Mendelian Genetics Terms • Homozygous • Heterozygous • Phenotype • Genotype • Punnett square • Monohybrid cross • Testcross

  6. Testcross

  7. What happens if looking at two traits simultaneously? • Dihybrid cross x True-breeding Parent (P) F1 F2: 9:3:3:1

  8. Mendel’s Law of Independent Assortment • Each character is independently inherited – segregate independently during gamete formation • Practice dihybrid crosses • Use rules of probability to predict outcomes of genetic crosses

  9. http://www.biology.arizona.edu/mendelian_genetics/problem_sets/monohybrid_cross/monohybrid_cross.htmlhttp://www.biology.arizona.edu/mendelian_genetics/problem_sets/monohybrid_cross/monohybrid_cross.html

  10. More Complicated Situations… • Incomplete dominance

  11. Multiple Alleles IAIA = A; IAi = A IBIB=B; IBi = B IAIB= AB ii = O A, B – codominant i - recessive

  12. Other situations: • Pleiotropy – one gene affects several phenotypes • Epistasis – one gene affects the phenotypic expression of another gene • Polygenetic inheritance – additive effect of two or more genes on a single phenotypic character

  13. Recessively inherited disorders: albinism, cystic fibrosis, Tay-Sachs disease, sickle-cell anemia Dominantly inherited disorders: Achondroplasia, Huntington’s disease Human Disorders that follow Mendelian Patterns of Inhertitance

  14. Cystic Fibrosis

  15. Tay-Sachs Disease

  16. Achondroplasia

  17. Huntington Disease Late Acting – middle age Western Europeans

  18. Screening for inherited disorders

  19. Pedigrees

  20. Pedigree – Huntington disease

  21. Pedigree – Sickle cell anemia

  22. Chromosomal Theory of Inheritance Thomas Morgan Fruitflies 4 pairs of chromosomes Wild type phenotype Mutant phenotype White-eyed males only

  23. Sex-linked traits Located on Sex chromosomes: X or Y Females XX; Males XY X-linked recessive Hemophilia, color blindness

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